1. Field of the Invention
This invention relates generally to teletypewriter systems and more particularly to the subscriber or teleprinter terminal provided with a memory dial system.
2. Description of the Prior Art
In the teleprinter, wherein a teletypewriter subscriber communicates with other subscribers in the system by dialing the called subscriber's number, the dialing is effected by the rotary dial unit that generates dial pulses that are processed through an automatic teletypewriter exchange by any of the conventional switching systems to make connection to the called subscriber. In recent years the dialing has been effected by the use of "Touch-Tone" buttons or the equivalent allowing for the subscriber to merely punch-out the desired called subscriber's number rather than be effecting a rotary-dialing operation. When a subscriber fails to reach the called subscriber owing to busy lines or a busy called subscriber, appropriate means are provided to indicate to the calling subscriber that the call has not been completed. Such indications are for example: line occupied, "all trunks busy", or the like. In order to dial the call, the subscriber must repeat the entire called subscriber's number. Such numbers may include as few as two to as many as ten digits.
Providing a means to store and retain the called number has been a problem that has not been solved satisfactorily. In telephony systems provisions have been made for storing and retaining a called number in the central offices in the form of special memory banks with elaborate access channels requiring special codes and the like for storing and retrieving such data as required. Such arrangements are very costly and tie-up many switching channels within the central offices in order to accomplish the function of storing and retaining a called number that cannot be completed on a first try. Such central office storage means have not been completely accepted because of their complexity and expense. In the teletypewriter art the problem is more difficult primarily because the central office exchanges are of relatively smaller capacity and therefore are not economically feasible or oriented for justifying the more complex storage systems that have been used in the telephony art.
According to the present invention a memory device is provided at the subscriber's terminal and accordingly obviates the complexity of central office storage and retrieval operations.